The present invention relates to the art of earth boring and, more particularly, to a rotary rock bit with an improved bearing system having improved performance and longer lifetime characteristics. The present invention is an improvement in a rotary rock bit which includes a ball bearing system, i.e., a row of balls disposed in a pair of registering circumferential raceways, one in the bearing cavity of the cutter, and the other in the bearing pin on which the cutter rotates. Such bearings often fail in fatigue, by spalling of the raceways. Small pieces of metal are loosened from the raceways and find their way between other parts of the bearing, where they cause damage by being ground into the raceway or into confronting surfaces of other bearing elements. The net effect of such spalling is to reduce the life of the bearing, causing the cutter assembly to be retired before its cutting structure is completely dulled.
The bearing system of the present invention is especially adapted for use on that type of rotary rock bit popularly known as a three cone bit; however, its use is not restricted thereto and the bearing system of the present invention can be used in other rotary rock bits wherein an improved bearing system is required. A three cone bit must operate under very severe environmental conditions and the size and geometry of the bit is restricted by the operating characteristics. At the same time, the economics of petroleum production demand a longer lifetime and improved performance from the bit. In attempting to provide an improved bit, new and improved materials have been developed for the cutting structure of the cones thereby providing a longer useful lifetime for the cones. This has resulted in the bearing system being first to fail during the drilling operation. Consequently, a need exists for an improved bearing system to extend the useful lifetime of the bit.
In order to obtain high penetration rates with a rotary rock bit in some formations, it is necessary to apply heavy loads on the bit and to operate the bit at a moderate speed. With other formations only moderate loads are required but the bit must be operated at relatively high speeds. In addition, the rock bit is subjected to temperature extremes. The drilling operation may be conducted thousands of feet underground wherein elevated temperatures are encountered. In view of the foregoing circumstances, it can be appreciated that a bearing system for a rotary rock bit must include exceptional performance characteristics in a limited geometrical configuration. Since the entire drill string must be withdrawn to replace the bit when it fails, it is highly desirable to have the bearing system operate for an extended period of time.